E4440A Noise figure calibration

I am using E4440A spectrum analyzer to do noise figure measurement. I followed the calibration steps given in "Noise Figure Measurement Personality Guide", but the noise figure was not around 0 dB after calibration, and it was changing radically. So, what might be the problem? by the way, I used a agilent 346C noise source in the calibration. Thanks

As you can see, as your DUT noise figure goes to 0 and DUT gain goes to 0, your measurement uncertainty goes to infinity, which is what you are seeing.

The Y-factor method is the classic method that your instrument uses to do noise figure measurements. Going through this AppNote, the Y-factor method starts on page 8 in section 2.2, but the sections before that are a good background on the subject.

Also on page 8 on the bottom of the left hand column, you'll see the equation for how noise builds in a multi-stage system. The bottom paragraph states that "If the first stage gain G1 is high, that will make the second stage contribution small so that F12 will be mostly determined by F1 alone." To achieve the high gain of G1, a preamplifier is what is commonly used in this case, to make G1 very high so that the effects of the DUT is minimized. Do you have one?

As you can see, as your DUT noise figure goes to 0 and DUT gain goes to 0, your measurement uncertainty goes to infinity, which is what you are seeing.

The Y-factor method is the classic method that your instrument uses to do noise figure measurements. Going through this AppNote, the Y-factor method starts on page 8 in section 2.2, but the sections before that are a good background on the subject.

Also on page 8 on the bottom of the left hand column, you'll see the equation for how noise builds in a multi-stage system. The bottom paragraph states that "If the first stage gain G1 is high, that will make the second stage contribution small so that F12 will be mostly determined by F1 alone." To achieve the high gain of G1, a preamplifier is what is commonly used in this case, to make G1 very high so that the effects of the DUT is minimized. Do you have one?